1. Field of the Invention
The present invention relates generally to the fields of applied physics and chemical vapor deposition of thin metal films. More specifically, the present invention relates to a method of depositing a ruthenium seed layer on a substrate via chemical vapor deposition prior to depositing a ruthenium thin film via metalorganic chemical vapor deposition.
2. Description of the Related Art
In metal-insulator-metal capacitors, ruthenium is a preferred electrode material for capacitor dielectrics. As the next generation technology of VLSI and ULSI structures evolves, it will become necessary to use three-dimensional capacitors despite the metal capacitor dielectrics employed. This requires a thin film on the structures while maintaining a high dielectric constant and small leakage current. It is advantageous to use a chemical vapor deposition process (CVD) to effectively deposit such ruthenium thin films.
Chemical vapor deposition is a broad class of processes using controlled chemical reactions to create layers on wafers and is a key process in the development of ultra-large scale integrated circuit fabrication. Chemical vapor deposition of thin metal films realizes good step coverage and wafer-to-wafer repeatability on complicated topography. Additionally, the use of a metalorganic precursor for CVD ruthenium thin film deposition ensures a higher degree of wafer repeatability. However, for certain substrates, metalorganic CVD (MOCVD) of ruthenium films requires a seed layer.
Currently, ruthenium seed is deposited by physical vapor deposition (PVD) or sputtering. Physical vapor deposition of ruthenium seed is pure ruthenium and very smooth, a preferred characteristic for subsequent ruthenium thin film deposition. However, a PVD ruthenium seed layer is limited by poor step coverage when the critical dimension is small and the aspect ratio is high as is the case in ULSI structures. The benefits inherent in CVD deposition of thin films would accrue to a seed layer deposited in this manner; such CVD ruthenium seed layers would determine the quality of the subsequently deposited CVD ruthenium film, e.g., smoothness, adhesion of the ruthenium thin film and the degree of step coverage and conformality on structures such as MIM structure capacitors.
However, CVD deposition of a metal is not deposition of the pure metal as is the case in a sputtered metal, i.e, the resultant seed layer may contain oxygen. Although the amount of oxygen available during deposition determines the adherence of the seed layer to the substrate, the characteristics of a subsequently deposited thin metal film onto the seed layer are enhanced when the oxygen content of the seed layer is relatively low. This necessitates a CVD ruthenium seed layer being deposited in a manner such that the amount of oxygen available during seeding of the layer and the oxygen content of the end product can be regulated.
The prior art is deficient in the lack of effective means of depositing a ruthenium seed layer by chemical vapor deposition under specific conditions in order to control the characteristics of the seed layer and thereby those of a subsequently deposited ruthenium thin film. The present invention fulfills this long-standing need and desire in the art.
One embodiment of the present invention provides a method of forming a ruthenium seed layer on a substrate comprising the steps of vaporizing a ruthenium-containing compound; introducing the vaporized ruthenium-containing compound into a CVD apparatus; introducing oxygen into the CVD apparatus; maintaining an oxygen rich environment in a process chamber of the CVD apparatus for the initial formation of a ruthenium oxide seed layer; depositing the ruthenium oxide seed layer onto the substrate by chemical vapor deposition; and annealing the deposited ruthenium oxide seed layer in a gas ambient forming a ruthenium seed layer.
Another embodiment of the present invention provides a method of forming a ruthenium seed layer on a substrate comprising the steps of vaporizing a ruthenium-containing compound at a temperature of about 200xc2x0 C. to about 400xc2x0 C.; introducing the vaporized ruthenium-containing compound into a CVD apparatus; introducing oxygen into the CVD apparatus; maintaining an oxygen rich environment in a process chamber of the CVD apparatus for the initial formation of a ruthenium oxide seed layer wherein the oxygen to ruthenium ratio in said environment is from about 1:1 to about 100:1; depositing the ruthenium oxide seed layer onto the substrate by chemical vapor deposition; and annealing the deposited ruthenium oxide seed layer in a gas ambient selected from the group consisting of H2/N2, H2 and H2/Ar and wherein said annealing occurs at about 200xc2x0 C. to about 600xc2x0 C. thereby forming a ruthenium seed layer.
Another embodiment of the present invention provides a method of forming a ruthenium seed layer on a substrate comprising the steps of vaporizing a ruthenium-containing compound at a temperature of about 200xc2x0 C. to about 400xc2x0 C.; introducing the vaporized ruthenium-containing compound into a CVD apparatus; introducing oxygen into the CVD apparatus; maintaining an oxygen rich environment in a process chamber of the CVD apparatus for the initial formation of a ruthenium oxide seed layer wherein the oxygen to ruthenium ratio in said environment is from about 1:1 to about 100:1; depositing the ruthenium oxide seed layer onto the substrate by chemical vapor deposition such that the ruthenium oxide is RuOx wherein x is about 2; and annealing the deposited ruthenium oxide seed layer in a gas ambient selected from the group consisting of H2/N2, H2 and H2/Ar; wherein said annealing occurs from about 200xc2x0 C. to about 600xc2x0 C. wherein the ruthenium is RuOy with y less than 2 thereby forming a ruthenium seed layer.
Another embodiment of the present invention provides a method of forming a ruthenium thin metal film using a metalorganic precursor comprising the steps of forming a ruthenium seed layer on a substrate by the method(s) disclosed above; vaporizing the metalorganic precursor; and depositing the pure ruthenium thin metal film on the ruthenium seed layer by metalorganic chemical vapor deposition.
Other and further aspects, features, and advantages of the present invention will be apparent from the following description of the presently preferred embodiments of the invention given for the purpose of disclosure.